1. Field of the Invention
This invention relates to a serial image recording apparatus for recording characters, images or the like on a recording medium by scanning it with a recording head in a state in which the recording head faces the recording medium. More particularly, the invention relates to a shuttle-type recording apparatus in which a plurality of recording heads disposed at a predetermined interval can perform recording on corresponding ones of divided recording regions.
The invention is particularly suitable for use with a recording apparatus for performing recording by providing the surface of a recording medium with color materials based on image data, and is more suitable for an ink-jet recording apparatus for performing recording by discharging recording ink liquids as the color materials.
The present invention can be applied to all apparatuses which use a paper, a cloth, a leather, a nonwoven fabric, an OHP (overhead projector) sheet, a metal or the like as a recording medium. These apparatuses include, for example, business machines, such as printers, copiers, facsimile apparatuses and the like, and apparatuses for industrial production.
2. Description of the Related Art
A serial recording method in which recording is performed by scanning the surface of a recording medium with a recording head is widely used for various kinds of recording apparatuses because, for example, it is less expensive than a recording method using a full-line head which covers the entire width of a recording medium, such as recording paper or the like.
As serial recording apparatuses for coloring color materials in a recording medium, apparatuses for causing heating elements of a thermal print head to operate on dedicated thermosensitive paper, and apparatuses for performing recording by optically coloring dedicated photosensitive paper are known. Various methods for performing recording by providing a recording medium with color materials using a recording head have been practically used or proposed. Such methods include, for example, an impact recording method for causing an ink ribbon, in which an ink liquid is impregnated as a color material, to be in pressure contact with a recording medium by printing wires, a heat fusion transfer recording method or a heat sublimation transfer method for transferring ink by causing heating elements of a thermal print head to operate on an ink-ribbon head coated with a solid color material, and an ink-jet method for performing recording by discharging a recording ink liquid.
Recently, from the viewpoint of performing recording on ordinary paper, the recording method for providing color materials is mainly adopted. Particularly, the ink-jet recording method has advantages, such as low noise, low running cost, the capabilities of providing a small apparatus and recording on ordinary paper, the ease of color printing, and the like, and is generally used in recording apparatuses, such as printers, copiers and the like.
In the serial recording method, a recording head having recording elements, such as discharging ports or the like, capable of performing recording only within a relatively small range is disposed on a carriage and recording is performed by sequentially scanning a recording medium with the head. Hence, it is rather difficult to increase the recording speed, and high-speed printing has been a task for the serial recording method.
In order to increase the speed of image recording, various attempts have been proposed and practically used, such as an attempt to increase the recording width of a recording head (the range of arrangement of recording elements), an attempt to shorten the scanning time by increasing the speed of the carriage and the recording frequency, and an attempt to perform recording by bidirectional scanning. However, all of such methods have their limitations. For example, in order to increase the recording width, it is necessary to improve accuracy in the production of the head, thereby increasing the cost of the recording head, and the capacity of a printing buffer for temporarily storing recording data increases, thereby increasing the cost of the apparatus. Hence, such an approach is disadvantageous from the viewpoint of the cost.
In the method of causing coloration utilizing heat and in the method of providing color materials, particularly when the recording width is large, the necessity of means for preventing degradation of recording quality and the damage of the recording head due to the self heating of the recording head increases. In the ink-jet recording method of using a recording ink liquid from a recording head that does not contact a recording medium, if a recording head having a large recording width is used, complicated means for preventing degradation of recording quality due to undulation (cockling) of the recording medium caused by absorption of water in the ink is required. When increasing the recording frequency, it is necessary to increase the scanning speed of the carriage in order to maintain a certain pixel density. In such a case, the load of a driving source increases, and there is the possibility that recording quality is degraded due to oscillation of ink within the recording head caused by high-speed scanning of the carriage.
A relatively effective method for increasing the speed of a serial image recording apparatus is disclosed, for example, in Japanese Patent Laid-Open Application (Kokai) No. 50-81437 (1975) (U.S. Pat. No. 4,272,771). In this application, in order to simultaneously performing printing on left half and right half portions of a printing line, a left-side print head assembly and a right-side print head assembly supported by a carriage mechanism are used, thereby substantially doubling the printing speed. This application also states that a higher recording speed can be realized by increasing the number of the print head assemblies to at least three or by performing bidirectional recording.
However, in most of the conventional approaches disclosed in the above-described application and the like, the recording region is divided from the viewpoint of performing high-speed recording. Accordingly, a configuration in which an overlapped region where a plurality of heads perform scanning in an overlapped state is positively taken into consideration has not been disclosed. From the viewpoint of high-speed recording, an overlapped recording region must be removed as much as possible.
When performing recording on divided recording regions by taking respective shares in recording by a plurality of heads, recording on a sheet of a relatively large size can be performed at a high speed. Even in such a case, however, it is desirable to minimize the size of the apparatus.